Towards Predictable Precision Manipulation of Unknown Objects with Underactuated Fingers

This paper describes a new concept in underactuated hand design, motivated by a study of parallel mechanisms. Inspired by the end-effector motion and system reconfiguration in parallel wrists, we propose a morphology of fingers such that during fingertip precision manipulation the instantaneous screw axes, which describe the displacement of the grasped object respect to the palm of the hand, always intersect at the same known fixed point regardless of the object’s particularities. A physical hand was built to evaluate the feasibility of the design concept in improving precision manipulation capabilities while preserving power-grasping functionality. The tendon-driven hand is underactuated, with one actuator for each of the two-degree-of-freedom fingers, and passive rotary fingertips are used to minimize slip at contact points during manipulation. Experimental results with the hand demonstrate the effectiveness of the concept, thus encouraging further research in the area.